On Monday, the Chinese consulate in San Fransisco, citing new pandemic-related cleaning requirements, prompted an order requiring the Delta Airlines flight, which was scheduled from Seattle to Shanghai, to turn back mid-air. 

An emailed statement said the new orders at Shanghai Pudong International Airport "require significantly extended ground time and are not operationally for Delta."

Amid the already-strict COVID-19 travel restrictions following an outbreak in the city of Xi'an, the Chinese COVID rules weren't clear at the time. But it seems that China has tightened the regulations ahead of the Winter Olympics, scheduled six weeks from today. 

Xi'an, which is 1,000 kilometers (600 miles) southwest of Beijing, has reported more than 300 new cases over the weekend. The city's population of 13 million has been locked down, with the rules having only one person allowed to go out every two days to shop for the grocery and necessities.

The consulate in San Francisco did not name Delta. But, a short statement released on Sunday said that various flights from the U.S to China had been delayed and canceled in these recent days, and some were even forced to turn back around halfway to their destinations. 

The consulate "had made a strict representation to the airline," the statement said.